Process for oxidizing durene to durylic acid



United States Patent 2,892,868 PROCESS FOR OXIDIZING DURENE TO DURYLIC ACID more particularly to the production of durylic acid by the liquid phase oxidation of durene with an oxygencontaining gas while in contact with a cobalt catalyst.

The primary purpose of this invention is to provide a process whereby high yields of durylic acid are obtained from durene while minimizing the concomitant production of other acids derivable from the oxidation of durene, particularly pyromellitic acid, or the dimethyl phthalic acids. Another purpose of this invention is to obtain a more selective yield of durylic acid from the oxidation of durene by reducing the yield of other oxygenated products such as aldehydes and other neutral materials. In oxidizing durene to durylic acid, the durylic acid obtained is useful as an intermediate in the preparation of pyromellitic acid. Pyromellitic acid, obtained by the nitric acid oxidation of durylic acid, is useful in preparing alkyl resin fibers and plasticizers.

In accordance with our invention, we have discovered that when operating under controlled process conditions of temperature, oxygen absorption and pressure, high yields of durylic acid are obtained from the cobalt catalyzed liquid phase air oxidation of durene. The oxidation is controlled at a temperature within the ranges of from about 300 to 400 F., preferably about 340 to 360' F., and oxygen is supplied to the extent that the conversion corresponds to about 1.1 to 1.8, and preferably about 1.3 to 1.6 moles of oxygen absorbed per mole of durene charged. Advantageously, the oxygen-containing gas may be introduced to the liquid reaction mixture by any means effecting finely dispersed air bubbles, such as a sparger, for example. In order to obtain high yields of durylic acid the liquid phase oxidation of durene must be carried out using these process conditions. For example, durene was converted to durylic acid at a temperature of about 350 F. with an oxygen absorption of 1.2 moles to yield more than 20% more of the acid per pass than at a temperature of 450 F. with 1.9 moles of oxygen absorption or at a temperature of 350 F. with .92 mole of oxygen absorption. Thus, the amount of durene converted to durylic acid is a function of the oxygen absorbed per mole of durene and the temperature of oxidation. High yields at good conversion rates are desired to avoid an increased burden when recycling unconverted durene.

The reaction pressure employed in the present process should be sufiicient to maintain the reaction in the liquid phase and is usually within the range of from about 50 to 500 p.s.i.g., and preferably within a range of from about 200 to 400 p.s.i.g. The oxidation of durene may be carried out in the liquid phase at atmospheric pressure since the boiling point of durene is 383 F.; however, at this pressure, low yields result and the rate of oxidation is diminished due to the air feed rate being limited by intense foaming. With a superatmospheric pressure under the process conditions hereinbefore described, the oxidate does not manifest any substantial tendency to foam, thus eifecting higher flow rates, higher yields, and a considerable saving in time.

As previously stated, the liquid phase oxidation of durene is carried out in the presence of a cobalt containing catalyst. In the selection of the catalyst, any

2,892,868 Patented June 30, 1959 cobalt salts which are soluble or dispersible in the reaction medium may be employed, and such salts as cobalt acetate, cobalt naphthenate, and cobalt toluate are preferred, particularly cobalt toluate. The amount of catalyst employed will be such as to afford a substantial catalytic effect and in general will usually be about from 0.05 to 5% by weight of the total charge.

The reaction is conveniently carried out in the usual type oxidation apparatus designed for an exothermic liquid phase operation. In a typical embodiment, mixtures of durene and cobalt p-toluate catalyst were charged to the reactor, the catalyst comprising about 0.5% of the charge. Heat was applied until the desired temperature was reached, at which time dry air was admitted to the reactor by means of a pressure regulator and a calibrated rotameter. An outlet tube leading from the top of the reactor to a Dry Ice trap served as an air condenser and was wound with an electrical tape to prevent plugging by solidified durene. After the desired amount of air was blown through the reaction mass, the reaction was stopped and the oxidate removed from the reactor and dissolved in ether. The acidic components were ex tracted with a base and then reprecipitated with acid. The ether solution from which the acids were extracted was washed, dried, and the solvent removed therefrom. This yielded a neutral fraction containing, among other things, durene and durylic aldehyde which upon recycle would have increased the yield. The crude durylic acid thus obtained (B.P. 193-206 C./33 mm.) can be further purified by distillation, recrystallization from benzene, by steam distillation, or by conversion to its methylester (B.P. 93-95 C./2 mm. n =1.5250).

The runs of the following examples were conducted in accordance with the above procedure and are given for the purpose of demonstrating the process of the present invention and the advantages thereof in converting durene to durylic acid.

Table I Run N 1 2 Pressure, p s i e 300 300 Temperature, F 400 350 Durene Charge, grams 150. 5 157 Mcogas oxlygen as Air Throughput per Mole Durene 6 7. 3

arge Moles Oxygen Absorbed 1. 7 1. 2 Rate of Air Throughput, fti/hour 8. 1 9. 0 Cobalt p-Toluate, Percent oi Charge (24.8% Cobalt). 40 38 Durylic Acid (corrected) g 84. 5 107.4 Yield, Wt. percent of Corrected Charge, per pass 66.3 80. 2

(theory 122.3%).

References Cited in the file of this patent UNITED STATES PATENTS 2,245,528 Loder June 10, 1941 2,509,855 Beach May 30, 1950 2,727,919 Saunders Dec. 20, 1955 OTHER REFERENCES J'annasch: Beil'steins Handbuch, vol. 9 (1926), p. 554. Gissmann: Beilstein's Handbuch, vol. 9 (1926) p. 554. 

1. THE CATALYTIC LIQUID PHASE OXIDATION OF DURENE TO DURYLIC ACID, WHICH COMPRISES OXIDIZING A FEEDSTOCK CONSISTING OF DURENE OF THE LIQUID PHASE WITH AN OXYGEN-CONTAINING GAS IN THE PRESENCE OF COBALT-CONTAINING CATALYST, AT A TEMPERATURE BETWEEN ABOUT 340 TO 360*F., A PRESSURE OF ABOUT 200 TO 500 P.S.I.G., AND UNTIL ABOUT 1.1 TO 1.8 MOLES OF OXYGEN HAVE BEEN ABSORBED PER MOLE OF DURENE CHARGED. 